In one known arrangement for synchronising the oscillator a passive tuned LC-oscillator has been used to provide the clock signal and this oscillator is started by means of a clock run-in signal which is transmitted at the beginning of each data line. Once started by the run-in signal the oscillator "rings" during the remainder of the data line.
In another known arrangement the oscillator is provided in the form of a crystal oscillator which oscillates at a frequency equal to the transmitted data rate. This frequency is then delayed to obtain four clock signals of different, non-overlapping phases and each is compared with a transmitted clock reference, the best match being selected.
Both of the above known methods require expensive oscillating elements and also their performance is not entirely satisfactory.